Process for producing highly water-absortive polymers

Abstract

There is provided a process for producing a substantially water-insoluble, highly water-absorptive polymer which comprises subjecting an aqueous solution of a monomer comprising as a main component acrylic acid and/or its alkali metal salt to polymerization in the presence of a hypophosphorous acid compound.

What is claimed is: 
     
       1. In a process for producing a substantially water-insoluble, highly water-absorptive polymer which comprises subjecting an aqueous solution of a monomer comprising as a main component acrylic acid and/or its alkali metal salt to polymerization conditions effective for producing water-insoluble, water-absorptive polymers, the improvement comprising effecting said polymerization in the presence of a hypophosphorous acid compound and from about 0.001 to about 0.5 percent by weight of a crosslinking agent. 
     
     
       2. The process according to claim 1, wherein the monomer comprises as a main component sodium acrylate having a neutralization degree of 50 to 95%. 
     
     
       3. The process according to claim 1, wherein the polymerization is carried out with the use of a radical polymerization initiator. 
     
     
       4. The process according to claim 3, wherein said initiator is a persulfate or an azo compound. 
     
     
       5. The process according to claim 3, wherein said initiator is used in the form of a redox type initiator in combination with a reducing agent. 
     
     
       6. The process according to claim 1, wherein the hypophosphorous acid compound is selected from the group consisting of hypophosphorous acid, sodium hypophosphite, potassium hypophosphite, calcium hypophosphite, barium hypophosphite, and ammonium hypophosphite. 
     
     
       7. The process according to claim 1, wherein the hypophosphorous acid compound is used in an amount of 10 to 10,000 ppm based on the aqueous solution of a monomer. 
     
     
       8. The process according to claim 7, wherein said amount is 100 to 2,000 ppm. 
     
     
       9. The process according to claim 1, wherein the concentration of acrylic acid and/or its alkali metal salt in the aqueous monomer solution is 20 to 80%. 
     
     
       10. The process according to claim 9, wherein said concentration is 30 to 60%.